The condensation reaction of an olefin or a mixture of olefins to form higher molecular weight products is widely known and practiced. This type of condensation reaction is referred to herein as an oligomerization reaction, and the products are low molecular weight oligomers which are formed by the condensation of up to 12, typically 2, 3 or 4, but up to 5, 6, 7, or even 8 olefin molecules with each other. “Oligomerization” refers to a process for the formation of oligomers and/or polymers. Low molecular weight olefins (such as, for example, ethylene, propene, 2-methylpropene, 1-butene and 2-butenes, pentenes and hexenes) may be converted by oligomerization over, for example, a solid phosphoric acid catalyst (commonly referred to as “sPa” catalyst) or a molecular sieve catalyst (e.g., a zeolite catalyst), to an oligomer product.
Oligomer products are valuable components of high-octane gasoline blending stock that may be used or blended into a distillate type liquid fuel or as a lubricant, or as a starting material for the production of chemical intermediates and end-products. Such chemical intermediates and end-products include high purity hydrocarbon fluids or solvents, alcohols, detergents/surfactants, and esters such as plasticizer esters and synthetic lubricants.
A number of catalysts may be used in such oligomerization processes. For example, industrial oligomerization reactions employing molecular sieve catalysts are generally performed in a plurality of tubular or chamber reactors, similar to those processes employing sPa catalysts. With sPa catalysts, the pressure drop over the catalyst bed(s) increases gradually over the duration of the run, due to coking and/or swelling of the catalyst pellets and the reactor run is typically terminated when a maximum allowable pressure drop over the reactor is reached. Molecular sieve catalysts do not show pressure drop increases similar to sPa catalysts. Oligomerization reactors using molecular sieve catalysts are therefore characterized by longer reactor run lengths and are typically decommissioned when the catalyst activity has dropped to an unacceptably low level. With these catalysts, the reactor run length that can be achieved is therefore much more sensitive to compounds, impurities, or contaminants in the feedstreams that deactivate the catalyst, such as catalyst poisons.
Strong bases, such as the proton bases or Bronsted bases, are known poisons for many of the oligomerization catalysts that are acidic, for example, molecular sieve catalysts. Such bases in hydrocarbon streams are often nitrogen containing compounds, such as amines, amides, and/or nitriles, and they are typically removed from feedstreams for oligomerization reactions and other hydroprocessing reactions. Such organic nitrogen-containing Bronsted bases are characterized by at least one hydrogen atom bound to the nitrogen atom and are known proton acceptors. Other organic nitrogen components do not have any hydrogen atoms bound to the nitrogen and the nitrogen atom may have three bonds to 1, 2 or 3 surrounding carbon atoms. These nitrogen atoms however still have a free electron pair and therefore can still act as a base, termed a Lewis base. Lewis bases are known to be weaker bases as compared to Bronsted bases and therefore are sometimes considered less problematic to acid catalyzed processes. The past is replete with attempts to treat feedstreams prior to undergoing any hydroprocessing reaction.
For example, U.S. Pat. No. 4,973,790 discloses a process for oligomerization of C2 to C10 olefins over a zeolite catalyst comprising a feed pre-treatment step to remove basic nitrogen compounds. It is directed to the removal of amines such as di-ethanol-amine.
U.S. Pat. No. 4,153,638 discloses a process for polymerizing C2 to C5 olefins to form gasoline and distillate boiling range oligomer products in the presence of a metal-substituted synthetic mica montmorillonite catalyst.
U.S. Patent Application Publication No. 2002/103406 discloses a process for oligomerizing an olefin originating from an oxygenate to olefin process using a nickel based catalyst. The olefin stream has a low nitrogen content, as low as 0.3 ppm by weight. This stream is therefore very suitable for oligomerization using nickel based catalysts because these catalysts are known to be particularly sensitive to poisons, such as nitrogen compounds.
U.S. Patent Application Publication No. 2004/0097773 discloses a process for oligomerizing isobutene. It discloses the removal of nitrogen components from the feed stream including acetonitrile and N-methyl-pyrrolidone. Both compounds are nitrogen-containing Lewis bases. The catalyst used in U.S. Patent Application Publication No. 2004/0097773 is a solid, acidic ion exchange resin in which some of the acidic protons have been exchanged for a metal ion.
U.S. Pat. Nos. 7,205,448, 7,744,828, and U.S. Patent Application Publication No. 2007/0213575 disclose the removal of nitrogen compounds, including a number of Lewis base compounds such as acetonitrile, N-methyl-pyrrolidone, morpholines such as N-formyl morpholine, pyridine and/or quinoline, from feedstreams.
Other background references include U.S. Patent Application Publication Nos. 2005/0137442, 2005/0152819, 2008/0312484, U.S. Pat. No. 6,160,193, GB 1,131,989, and WO 2000/71494. Thus, many catalysts and their respective catalyst lives may be profoundly influenced by contaminants, such as, for example, nitrogen containing compounds (e.g., nitriles) and other contaminants such as for example, sulfur containing compounds, in feedstreams. Therefore, there remains a long-standing need to address the problems associated with basic contaminants in feedstreams.
In response, solvent extraction processes have been used in the past to treat certain feedstreams. For example, U.S. Pat. No. 5,675,043 discloses processes for treating a hydrocarbon blend containing nitrogen-containing compounds with a solvent having a Hansen polar solubility parameter to effect removal of a portion of said nitrogen-containing compounds therefrom. (See claim 1). Example 1 exemplifies the use of sulfolane. Nagai et al., Isolation of Nitrogen-containing Heterocyclic Compounds Contained in Coal Tar Absorption Oil Fraction with Solvent Extraction, Sekiyu Gakkaishi (Journal of the Japan Petroleum Institute), 43 (5), 339-345 (2000), discloses using aqueous solutions of methanol or tetrahydrothiophene-1,1-dioxide (sulfolane) to remove heterocyclic compounds containing nitrogen atoms from coal tar oil absorption oil fractions. In other areas, SU 1086006 discloses using a metal chloride such as NiCl2 in an organic solvent such as propylene carbonate or dimethylsulfoxide or dimethylformamide to remove nitrogen compounds from petroleum products by complexing the metal chloride with the nitrogen compounds. Despite these past endeavors, there remains a need to improve upon the removal of nitrogen containing compounds, such as, for example, one or more nitriles and optionally other components, from feedstreams of olefins and paraffins to allow for downstream processing such as hydroprocessing to occur more efficiently.